1. Field of the Invention
The present invention relates to a process for production of a crosslinkable styrene derivative polymer having narrow molecular weight distribution.
2. Description of the Prior Art
Various crosslinkable polymers are currently made by polymerization of a vinyl compound using a radical polymerization initiator. These polymers are used in various fields such as coatings or resists. In many cases, a crosslinkable functional group is introduced in these polymers to improve chemical or physical properties.
When a polymer contains a self-crosslinkable functional group which can be converted into a three-dimensional crosslinked resin by heating the polymer itself or by adding a curing catalyst to the polymer and heating the mixture; or when a polymer contains a crosslinkable functional group which can be converted into a three-dimensional crosslinked resin by using, in combination, a curing agent reactive with the crosslinkable functional group, the polymer is defined as a "heat-crosslinkable" resin, as well as a phenol resin, an epoxy resin or a melamine resin.
When a polymer contains a self-crosslinkable functional group which can be converted into a three-dimensional crosslinked resin by irradiating the polymer itself or by adding a curing catalyst to the polymer and exposing the mixture to actinic radiation (e.g. sunlight, an electronic beam or X-ray), or when a polymer contains a crosslinkable functional group which can be converted into a three-dimensional crosslinked resin by using, in combination, a curing agent reactive with the crosslinkable functional group and actinic radiation, the polymer is defined as a "photo-crosslinkable" resin.
The above-mentioned heat- or photo-crosslinkable styrene or styrene derivative polymers have previously been prepared by polymerization of a vinyl compound using a radical polymerization initiator. The polymers obtained by this process, however, generally have a broad molecular weight distribution and accordingly have limited applications because of the difficulty of rheology control. Furthermore, it is basically difficult to control the distribution of a crosslinkable functional group in a polymer molecule during polymerization, since the distribution of a crosslinkable functional group in a polymer molecule is determined according to the reactivity and composition of monomers during polymerization.
It would be highly desirable to obtain a polymer having a crosslinkable functional group, a narrow molecular weight distribution and a controlled functional group distribution, in order to solve the above-mentioned problems. It is also desirable to produce a polymer having a molecular weight distribution of smaller than 2 [the molecular weight distribution is generally expressed by the ratio (Mw/Mn) of weight-average molecular weight (Mw) and number-average molecular weight (Mn)]. Polymerization of a vinyl compound is also possible by using polymerization systems other than radical polymerization, i.e. an ionic polymerization or a coordination polymerization. However, in using ionic or coordination polymerization, a highly reactive polymerization initiator is typically used, and the presence of impurities (e.g. small amounts of water and active-hydrogen-containing compound) in the reaction system hinders the polymerization reaction and allows the produced polymer to have a broad molecular weight distribution.
U.S. Pat. No. 5,322,912 discloses a process for production of a thermoplastic resin having narrow molecular weight distribution. The polymer obtained by this process, however, does not contain a crosslinkable functional group and accordingly cannot be used as a crosslinkable resin.